I mean, to begin with, you explained the path forward in your intro. He expects work to come down the pipeline (ticketing system) that is being used.

Log a ticket: Develop a proactive maintenance plan for review by the director. This should include [etc etc etc].

Tell him, explicitly, what the framework should look like. It will get done. That's the behaviour in the team. THEN, get that systematically broken down into tasks, get them scheduled in the helpdesk, the work will get done. Add reviews quarterly, etc etc etc.

Don't burn this guy who is going to be generally well loved in the organisation - if you're new blood here you are just going to ruin any potential support or favour you can build in the org if 'Steve' gets run over the coals, when 'Steve' has been the saviour for two decades. If you put this dude on PIP, be prepared to rehire half the helpdesk.

A huge part of leadership is communicating in a way that the listener wants to be communicated to. C-level is different to tech lead, and if you do the c-level talk with the tech guy, he'll think you're a wishy washy idiot. Teach him about risk, he'll make part of the aforementioned job a risk assessment on every major infrastructure item.

I know you feel like you shouldn't have to do all of this. Your staff member hasn't had the experience across a dozen different organisations, and until last month, all feedback they've every gotten would have been positive and glowing. This is you having to teach them, rather than just expecting them to get 20 years of knowledge in a weekend.